A growing donor organ shortage has created a renewed interest in xenotransplantation, the use of organs from members of different species. This project will focus on the cellular and immunopathological mechanisms that occur in a xenotransplantation model. The use of pigs as organ donors for human transplantation is limited by a violent hyperacute rejection response that occurs within minutes. The events that lead to this rejection response are not well defined. An ex-vivo cardiac perfusion model has been designed that allows a pig heart to be perfused with fresh whole human blood. Interventions will be aimed at two components involved in the hyperacute rejection response, namely natural antibody and complement. Antibody (IgG and IgM versus IgM alone) will be selectively depleted from human serum by column absorption and time to rejection or cessation of heart function will be compared to control experiments. Additional studies will focus on depletion or inhibition of specific components of the complement system with the use of anti-C5 and anti-C8 monoclonal antibodies as well as specific enzymatic inhibitors directed at C3 convertase. Further experiments will be designed based on the results of these studies and these results will be used as a basis on which to conduct in-vivo pig to baboon heterotopic cardiac transplantation experiments.